The present disclosure relates to a semiconductor integrated circuit, and more particularly, to a fuse option circuit of a semiconductor integrated circuit.
Generally, a fuse option circuit is used in a semiconductor integrated circuit for various purposes. For example, the fuse option circuit is widely used for storing chip identification (ID), repairing a defective semiconductor memory cell, and properly setting an internal voltage by trimming. Programming methods for a fuse option circuit can be classified into a laser blowing method and an electrical blowing method. In a laser blowing method a fuse is blown by irradiating the fuse with a laser. In an electrical blowing method, a fuse is electrically cut by applying a predetermined current to the fuse to change the resistance of the fuse. Particularly, the electrical blowing method can be used after a semiconductor chip is packaged. The electrical blowing method is also called an electrical fuse (eFUSE) method. An example of a fuse option circuit using an electrical fuse is disclosed in U.S. Pat. No. 6,498,526, entitled “FUSE CIRCUIT AND PROGRAM STATUS DETECTING METHOD THEREOF”. However, when an electrical fuse (or “efuse”) is used, it is difficult to determine whether the electrical fuse is cut, as compared with the case where a laser blowing method is used. Furthermore, when an uncut electrical fuse is programmed, the electrical fuse can be undesirably cut by an impact or noise after a packaging process. In addition, an electrical fuse can be undesirably programmed by a large current applied to the electrical fuse in a die sort test process, regardless of the existence of a programming command.
FIG. 1 is a sectional diagram illustrating a conventional semiconductor integrated circuit device 10 including an electrical fuse formed after a packaging process. Referring to FIG. 1, the packaged semiconductor integrated circuit device 10 includes metal pins for electric connection with external devices. PAD_0 through PAD_n of an integrated circuit die 20 are connected to Lead_0 through Lead_m through metal wires. The integrated circuit die 20 includes a fuse block 21. The fuse block 21 includes a plurality of efuses and other circuits used for fuse programming and reading. Generally, fuse programming is performed prior to a packaging process for storing a chip ID, repairing a defective cell, and trimming for analog circuits, for example. A fuse program is generally a one-off program. Therefore, after the PAD_2 is used to receive a fuse program signal PGM (or a fuse program command) for fuse programming, the PAD_2 in not used. In a packaging process, the PAD_2, which is not connected to a pin for electric connection with an external device, is packaged using an insulation material. That is, the PAD_2, which is formed to receive a fuse program signal PGM, is not connected to an external device after a packaging process. Therefore, a program signal line connected between the PAD_2 and the fuse block 21 remains in a floating state.
However, since a semiconductor integrated circuit is formed on a semiconductor substrate, signal lines of the semiconductor integrated circuit have a relatively large parasitic capacitance and thus store an undesired electric charge or couple to other signal lines. Therefore, the program signal line, which is connected between the PAD_2 and the fuse block 21 to transmit a fuse program signal PGM, has an undesired parasitic capacitance Cpra. Furthermore, the parasitic capacitance Cpra of the program signal line can couple with other adjacent signal lines, resulting in noise. In addition, an electric leakage charge can be stored in the program signal line because of the parasitic capacitance Cpra. For these reasons, the electric potential of the program signal line can be increased. When the electric potential of the program signal line is increased larger than a desirable level, the electric potential of the program signal line results in the same effect as a fuse program signal PGM. For example, a driver device (not shown) connected to an end of the program signal line can be turned on when the electric potential of the program signal line is increased by accumulated electric charge. That is, in a mounted semiconductor circuit device, a fuse can be undesirably programmed. Moreover, before a packaging process, a fuse can be programmed by a high voltage Vpp applied to the fuse block 21, even though a fuse program signal PGM (or a program command) is not input.